Purification of chloroacetyl chloride by azeotropic distillation

ABSTRACT

Monochloroaceyl chloride can be separated efficiently from dichloroacetyl chloride by adding an azeotrope-forming agent to the mixture and distilling off the monochloro acid chloride azeotrope. Azeotrope formers have a boiling point of about 90*130*C. and are hydrocarbons, halogenated hydrocarbons and aliphatic ethers.

United States Patent [1 1 [111 3,763,023

Horsley Oct. 2, 1973 [54] PURIFICATION OF CIILOROACETYL 2,889,365 6/1959Prill 260/544 Y CHL Y AZEOTROPIC 3,576,860 4/1971 Zazarism 3,686,302 81972 Opitz 260/544 Y DISTILLATION Lee II. I-Iorsley, Midland, Mich.

The Dow-Chemical Company, Midland, Mich.

Filed: May 30, 1972 Appl. No.: 257,833

Inventor:

Assignee:

US. Cl 203/63, 203/67, 203/68,

' 203/69, 203/70, 260/544 Y Int. Cl C07c 53/20, BOld 3/36 Field ofSearch 260/544 Y; 203/63, r 203/67, 68, 69, 70

References Cited UNITED STATES PATENTS 2/1958 Lacey 260/544 Y PrimaryExaminer-Wilbur L. Bascomb, Jr. AttorneyWilliam M. Yates et al.

[57] ABSTRACT Monochloroaceyl chloride can be separated efficiently fromdichloroacetyl chloride by adding an azeotropeforming agent to themixture and distilling off the monochloro acid chloride azeotrope.Azeotrope formers have a boiling point of about 90l30C. and arehydrocarbons, halogenated hydrocarbons and aliphatic ethers.

5 Claims, N0 Drawings PURIFICATION OF CHLOROACETYL CHLORIDE BYAZEOTROPIC DISTILLATION BACKGROUND OF THE INVENTION This inventionrelates to a new chemical process and it concerns particularly a processfor separating chloroacetyl chloride from its mixture withdichloroacetyl chloride by azeotropie distillation.

Chloroacetyl chloride is normally made by chlorinating acetic acid witha sulfur or phosphorus chloride which yields as the crude product, thedesired chloroacetyl chloride mixed with small but appreciablequantities of under-chlorinated material and more or less of thedichlorinated acid chloride, depending upon the degree of chlorination.The under'chlorinated products are easily separable by distillation, butsince the two chlorinated acid chlorides have very close boiling points,separation of these compounds by simple distil lation is impractical.Substantial under chlorination essentially eliminates the dichloroacetylchloride, but this procedure involves the distillation and recycle of anuneconomically impractical amount of unreacted acetic acid and acetylchloride.

Chloroacetyl chloride forms lower boiling azeotropes with a number ofdissimilar compounds such as hydrocarbons, halogenated hydrocarbons andethers and dichloroacetyl chloride also forms lower boiling azeotropeswith these same compounds. However, in both cases, the correspondingazeotropes have boiling points about as close as do the acid chloridesthemselves. Therefore, azeotropic distillation appears to offer nobetter chance for effective separation of these acid chlorides thandistillation of the mixed chlorides alone.

SUMMARY OF THE INVENTION It has now been found quite unexpectedly thatchloroacetyl chloride can be separated efficiently from dichloroacetylchloride by adding to the mixture an azeotrope-forming compound anddistilling off its azetrope with the monochloro acid chloride. Operableazeotrope-forming compounds have a boiling point at atmospheric pressureof about 90-l 30C., preferably about 95l 20C., and are hydrocarbons,halogenated hydrocarbons and aliphatic ethers. A mixture of relatedcompounds such as a saturated aliphatic hydrocarbon fraction having aboiling range within the defined limits can also be used.

DETAILED DESCRIPTION The quantity of azeotrope-forming compound added tothe chlorinated acid chloride mixture is not a critical factor, for anysignificant amount will distill from the mixture as its azeotrope withchloroacetyl chloride and so effect a separation to the extent that itis present. Preferably, enough azeotrope-former is used to separateessentially all of the chloroacetyl chloride. A smaller amount willresult in incomplete recovery of chloroacetyl chloride while an excessrequires unnecessary distillation to remove it.

The distillation pressure is also not a critical condition. Preferably,the distillation is run at a pressure between about 10 mm. Hg andatmospheric pressure for reasons of distillate condensation efficiencyat lower pressures and increasing corrosion of equipment and thermaldecomposition of products at higher pressures.

The classesof azeotrope-forming compounds suitable for use in thisprocess can be divided into a numher of groups and subgroups. Thus,aliphatic, cycloaliphatic and aromatic hydrocarbons having normalboiling points within the defined range are operable. The aliphatichydrocarbons can be defined further as saturated, olefinic andacetylenic aliphatic hydro carbons. These can be branched or straightchain compounds. Examples of these various groups are nheptane,2,4,4-trimethyl-l-pentene, l-heptyne, 2- methylhexane, n-octane,2,4-dimethylhexane, methylcyclohexane, methylcyclohexene and toluene.For obvious reasons, hydrocarbons containing no aliphatic unsaturationare more desirable than their unsaturated analogs.

Similarly, the class of halogenated hydrocarbons includes halogenatedaliphatic hydrocarbons, haloge nated cycloaliphatic hydrocarbons andhalogenated aromatic hydrocarbons. In the same way, the halogen atom oratoms present can be one or more of the common halogens, fluorine,bromine, chlorine and iodine although the boiling point limitationsrestrict some of these subclasses to fluorinecontaining compounds. Examples include tctrachloroethylene, butyl iodide, l,l,2-trichloroethane,methylene bromide, ethylene chlorobromide, fluorotoluene,fluorochlorobenzene and the like.

The class of aliphatic ethers includes dialkyl ethers and unsaturatedaliphatic ethers.. Examples are diallyl ether, dipropyl ether, methylamyl ether, ethyl butyl ether and the like.

Of particular interest and advantage in the present process are thesaturated aliphatic hydrocarbons. These are not only stable andunreactive compounds, but they also have the property of mutualinsolubility with chloroacetyl chloride at moderately low tempera turesso that the distilled and condensed azeotrope can be separated bycooling into two liquid phases, thereby greatly facilitating theseparation of pure chloroacetyl chloride. A hydrocarbon fractionconsisting essentially of heptanes and octanes is a useful and readilyavailable member of this class.

This process can be operated either as a batch process or continuously.ln batchwise operation using an aliphatic hydrocarbon such as heptane,for example, the distilled azeotrope separates into two layers uponcooling to l0C. and the heavy chloroacetyl chloride layer is drawn offfor a finishing, distillation to remove any remaining heptane. The lightheptane layer is returned to the still if more is needed. When all ofthe chloroacetyl chloride has been separated, the light layer iswithdrawn until all heptane is removed from the still pot, leavingdichloroacetyl chloride as the residue.

Continuous operation is preferred for commercial practice. In this typeof operation, using the system above, the chloroacetylchloride-dichloroacetyl chlo ride mixture plus heptane can be fed into afractional distillation column at about its midpoint and thechloroacetyl chloride-heptane azeotrope distillate is condensed into aliquid separator where it is chilled to 10C. or below to form two liquidphases. Most of the heavy layer passes to a finishing column for removalof remaining heptane. Pure chloroacetyl chloride is drawn off from thebottom of the finishing column. Some of the heavy layer in the separatoris fed as needed into the top of the main distillation column as reflux.The

light (heptane) layer from the separator plus heptane from the finishingcolumn is also fed into the top of the main column while puredichloroacetyl chloride is drawn off from the bottom of the main column,conditions in this column being maintained such that the heptaneinventory remains principally in the upper part. When equilibrium hasbeen established, only small amounts of heptane need be added to themixed chlorinated acetyl chloride feed from time to time as makeup toreplace mechanical losses. The system thus operates with an essentiallyconstant inventory of heptane while the effluent products aresubstantially pure chloroacetyl chloride and substantially puredichloroacetyl chloride.

Both the batchwise and continuous modes of operation are similarlyoperable using octane or a heptaneoctane fraction as the hydrocarbonazeotropeforming agent. Cooling the distillate to about 20C. causesseparation into two liquid phases as described above.

Table 1 lists the boiling points and compositions at various absolutepressures for some of the preferred azeotropic systems discussed above.The figures can be used as a guide to operating conditions for eitherbatchwise or continuous operation of the separation process. These datawere determined by distilling small samples for analysis from thevarious mixtures.

TABLE I Acid Azeotroping Pressure Azeotrope Chloride Agent mm. Hg. B.p.C. Wt. Chloride Chloroacetyl chloride n-Heptane 760 90 45 Toluene 760I05 80 Toluene I 51 8O Dichloroacetyl chloride n-Heptane 760 95 37EXAMPLES l- The efficiencies of various azeotroping agents weredetermined by making up a mixture of 90% by weight chloroacetyl chlorideand 10 percent dichloroacetyl chloride and distilling small samples fromthis mixture with and without azeotropic agent at atmospheric pressureusing a 0.5 X 12 inch Vigreux column. Benzene is included as acomparative example of a related but ineffective compound outside thescope of the present invention. The data thereby obtained are listed inTable ll.

TABLE ll Wt. Dichloroacetyl Chloride Still Residue Azeotroping Agent N10 Distillate one 9 Benzene l0 l0 n-Heptane 10 4.1 Toluene l0 5.6n-Octane l0 4.] Diallyl Ether l0 2.] Tetrachlorocthylene l0 4.9

More complete separation is obtained by use of a more efficientdistillation column.

When the procedure of Examples 1-5 is repeated using methylene bromide,methylcyclohexane, 1,1,2- trichloroethane, fluorotoluene or methyl amylether as the azeotroping agent, similar results are obtained. Similarly,a paraffinic hydrocarbon fraction consisting essentially of heptanes andoctanes also provides efficient separation of chloroacetyl chloride fromdichloroacetyl chloride when it is used as the azeotropeformer. Such afraction, which is really a gasoline, behaves substantially as a singlehydrocarbon compound under the conditions of the process and nosignificant fractionation of the individual hydrocarbon species takesplace during the distillation.

I claim:

1. A process for separating chloroacetyl chloride from its mixture withdichloroacetyl chloride which comprises adding to said mixture anazeotrope-forming agent and distilling the azeotrope of chloro-acetylchloride and said agent from the resulting mixture, wherein said agenthas a boiling point at atmospheric pressure of about 90l30C. and is ahydrocarbon, a halogenated hydrocarbon or an aliphatic hydrocarbonether.

2. The process of claim 1 wherein the azeotropeforming agent is asaturated aliphatic hydrocarbon.

3. The process of claim 2 wherein the hydrocarbon is heptane.

4. A continuous process for separating chloroacetyl chloride from itsmixture with dichloroacetyl chloride which comprises continuouslyintroducing said mixture and saturated aliphatic hydrocarbon having anormal boiling point of about 90l C. into a first fractionaldistillation column, continuously removing therefrom a first distillatefraction and a first residue fraction, cooling said first distillatefraction at least to about l 0C., thereby causing separation into twoliquid layers, the cooled first distillate fraction consisting of anupper liquid layer which is essentially the saturated hydrocarbon and alower liquid layer which is substantially chloroacetyl chloride, saidfirst residue consisting essentially of dichloroacetyl chloride,continuously withdrawing said first residue, continuously returning saidupper liquid layer and a minor proportion of said lower liquid layer tothe first distillation column, continuously introducing the majorproportion of the lower liquid layer into a second fractionaldistillation column, continuously removing from said second column asecond distillate which is essentially saturated hydrocarbonchloroacetylchloride azeotrope and a second residue which is purified chloroacetylchloride, and returning said second distillate to said first column.

5. The process of claim 4 wherein the saturated hydrocarbon is heptane.

2. The process of claim 1 wherein the azeotrope-forming agent is a saTurated aliphatic hydrocarbon.
 3. The process of claim 2 wherein the hydrocarbon is heptane.
 4. A continuous process for separating chloroacetyl chloride from its mixture with dichloroacetyl chloride which comprises continuously introducing said mixture and saturated aliphatic hydrocarbon having a normal boiling point of about 90*-130*C. into a first fractional distillation column, continuously removing therefrom a first distillate fraction and a first residue fraction, cooling said first distillate fraction at least to about -10*C., thereby causing separation into two liquid layers, the cooled first distillate fraction consisting of an upper liquid layer which is essentially the saturated hydrocarbon and a lower liquid layer which is substantially chloroacetyl chloride, said first residue consisting essentially of dichloroacetyl chloride, continuously withdrawing said first residue, continuously returning said upper liquid layer and a minor proportion of said lower liquid layer to the first distillation column, continuously introducing the major proportion of the lower liquid layer into a second fractional distillation column, continuously removing from said second column a second distillate which is essentially saturated hydrocarbonchloroacetyl chloride azeotrope and a second residue which is purified chloroacetyl chloride, and returning said second distillate to said first column.
 5. The process of claim 4 wherein the saturated hydrocarbon is heptane. 